Animal use in scientific research is critical to understanding biomedical systems that lead to the development of useful drugs, therapies, and cures for diseases and pathologies. Mice are commonly used in biological research for many reasons: they are easily housed and maintained, they are relatively inexpensive, they reproduce quickly, their biological and behavior characteristics closely resemble those of humans, their various transgenic models are available, etc. Approximately 20-30 million mice are used each year in the United States for biological and medical research; mice are used in research much more than any other animals (Anft M. Of Mice and Medicine, 2008 Johns Hopkins Magazine, Vol. 60).
For many experiments, it is imperative that procedures are conducted using alert, freely moving mice. This is generally achieved using a tether, which allows fluids or electrical connections to be sampled or administered to the animal. However, tethers are often heavy for a small animal because they need to be sufficiently long to allow connections between the animal in the cage and a device located outside of the cage. To improve freedom of movement, a swivel or commutator is generally used to connect the animal and the infusion or sampling device. However, electrical commutators are a source of electrical noise that can lead to data artifacts, and fluid swivels are often problematical as they are often stiff and subject to leaks and blockages. Using telemetric devices and miniature pumps may eliminate the need for swivels in the system, but such devices restrict the animal's movement due to the effects of their weight (i.e., the smallest telemetry transmitter weighs ˜4.6 grams or ˜20% of the average mouse's body weight). Further, these devices are often implanted intraperitoneally (i.p.), which is considered a major surgery that could cause post-surgical complications and interfere with the results of the experiment. The present invention is therefore directed to developing a system that can provide a reliable interface for animals and permit a high level of activity.
At present, several prior art systems are commercially available to provide interface for laboratory animals. The following is a brief description of existing systems.
Tethering Systems for Recording EEG and EMG
Pinnacle Technology (Lawrence, Kans.) offers a tether system for electroencephalogram and electromyogram recordings in mice. In this system, a low-torque commutator is used to release tangled wires during the mouse movement. This system is similar to most handmade systems used in research laboratories. To minimize the pressure that wires can cause on the mouse, lightweight wires are needed. However, it is difficult to make such wires because they must be protected with a metallic spring or plastic cover to prevent mice from biting them. Therefore, some pressure on the mouse is expected in this type of system, and this pressure will change depending on the position of the mouse in the cage. Animal's mobility in this system also depends on the mechanical resistance of the electrical commutator in the system. A stiff commutator can significantly restrict animal's movement in this type of system.
Tethering Systems for Infusion Test Substances
Instech Solomon (Plymouth Meeting, Pa.) and Harvard Apparatus (Holliston, Mass.) offer polycarbonate cages designed to house tethered rodents during short-term infusion and microdialysis experiments. These cages are made in a circular shape to avoid the tangling of tethers, which is more likely in shoebox-type cages. These cages are frequently used with counter-balanced lever arms to reduce the pressure of the infusion line on the animal. The presence of counter-balanced lever arms may help to reduce weighted pressure on the animal by the tether, but it cannot eliminate it because the animal changes its position in the cage. This type of system is usually recommended for short-term infusions, although it can be also used for longer infusions. Similarly to any other traditional tethered system, this one restricts animal's movement to some degree, which mainly depends on the weight of the tether and stiffness of the commutator.
Telemetry Devices and Miniature Pumps
Currently, the smallest EEG/EMG telemetry transmitters are produced by Data Sciences International (DSI; St. Paul, Minn.). The F20-EET transmitter allows for the recording of 2 EEG channels and weighs about 4 grams. This is about 20% of the weight of an average mouse, and is likely to restrict the mouse's mobility.
Osmotic pumps weigh as little as 0.4 grams (Alzet osmotic pumps, Cupertino, Calif.). Such a lightweight device is not expected to significantly reduce the mouse's movement. However, osmotic pumps are typically implanted i.p. with infusion lines placed under the skin, which could be disturbing or stressful for the animal.
Fiber-Optic Connections with the Mouse
In recent years, optogenetics has become a very powerful tool for assessing the physiological effects of activation or inhibition of specific neuron types in animals. Many companies offer optogenetics hardware. Currently, however, there is no commercially available equipment that provides the capability of a fiberoptic interface in combination with an electroencephalogram interface in freely moving animals. Some laboratories have designed their own systems for this purpose, but these systems are often bulky and restrict movement of a mouse. For example, stimulation of the thalamic reticular nucleus in vesicular gamma-aminobutyric acid transporter (VGAT)-channelrhodopsin-R2 (ChR2) mice produced state-dependent neocortical spindles (Halassa M. M., Siegle J. H., Ritt J. T., Ting J. T., Feng G., and Moore C. I. Selective optical drive of thalamic reticular nucleus generates thalamic bursts and cortical spindles, 2011, Nat. Neurosci. 14, 1118-1120), and stimulation of the locus coeruleus caused reversible behavioral arrests in ChR2-enhanced yellow florescent protein ((eYFP) mice (Carter M. E., Yizhar O., Chikahisa S., Nguyen H., Adamantidis A., Nishino S., Deisseroth K., and De Lecea L. Tuning arousal with optogenetic modulation of locus coeruleus neurons, 2010, Nat. Neurosci. 13, 1526-1533). Thus, some changes can be identified in mice whose locomotion is restricted by a large cable, but it could be difficult to observe subtle changes in behavior using such prior art systems.